Coupled granular/continuous medium for thermally stable perpendicular magnetic recording

We studied coupled granular/continuous (CGC) perpendicular media consisting of a continuous multilayer structure and a granular layer. The addition of Co/Pt multilayers decreased the nucleation field from 200 to -1800Oe and increased the squareness from 0.9 to 1.0. The moment decay at room temperature was significantly reduced from -4.8% to -0.05% per decade. At elevated temperatures, strong exchange coupling between a granular layer and a continuous layer is needed for thermal stability. The exchange-coupled continuous layer reduces thermal demagnetization as it effectively increases the grain size, tightens the grain distribution, and prevents the reversal of individual grains. Magnetic Force Microscope image showed a larger magnetic cluster size for the CGC structure. Compared to the CoCr₁₈Pt₁₂ medium, the CGC medium had 2.3dB higher output. However, the noise for the CGC medium increased with the recording density, while the noise for the CoCr₁₈Pt₁₂ medium remained constant from 4 to 15kfc/mm. Further optimization and noise reduction are still required for future high density recording.